Pathogenic microbes, organic and inorganic pollutants are commonly found in water of various sources. Disinfection and purification of water are required for direct human consumption as well as for industrial and agricultural processes that produce products to be consumed by human or animals. Numerous ways have been used to disinfect water, for example, chlorination and ozonation. It is already known that radicals produced by photocatalytic oxidation process can oxidize organic pollutants contained within water. Hydroxyl radical, one of the end products of the above photocatalytic reaction is an extremely potent oxidizing agent as compared to chlorine and ozone and is capable of oxidizing all organic compound. Furthermore, hydroxyl radicals also kill and breakdown microorganisms.
Photocatalyst that have been demonstrated for the destruction of organic pollutants in fluid include but are not limited to TiO2, ZnO, SnO2, WO3, CdS, ZrO2, SB2O4 and Fe2O3. Titanium dioxide is chemically stable and has a suitable bandgap for UV/Visible photoactivation, and is relatively inexpensive. Therefore, phototocatalytic chemistry of titanium dioxide has been extensively studied over the last thirty years for removal of organic and inorganic compounds from contaminated air and water.
WO 9637281 describes an apparatus for purifying air by means of an activated photocatalyst such as titanium dioxide. The apparatus comprises circulating means such as a fan to circulate air through a filter. The filter is coated with photocatalysts electrostatically fixed to a fibrous porous support with a light source to activate the photocatalyst. The shape of the filter is limited to flat shapes and only one side of the filter is exposed to light source. Though electrostatic force can hold photocatalyst strongly, however, loss of photocatalyst still occurs over time.
JP 11290844 discloses a water purifying apparatus that utilizes flowing force of the inward fluid to revolve a large number of ceramic balls having titanium dioxide applied to the surfaces with ultraviolet source fixed at the four sides of the container. Due to the random motion of the ceramic balls within the container, the radicals produced by photocatalytic oxidation reaction is not evenly distributed within the fluid and therefore reduces the efficiency of the purifying action.
JP 2000325750 describes a fluid purifying method that utilizes a freely movable support structure applied with photocatalyst. The support structure moves in response to the flowing force of an inflow fluid so that the purified fluid can be successfully torn off from the photocatalyst for more efficient purifying action. However, the method requires a sufficient flow force to initiate and sustain the movement of support structure which implies a relatively high flow rate of the fluid is required and therefore shorter contact time between fluid and free radicals.
It is an object of the present invention to provide an improved apparatus for purifying water.